Electronic ballistic computer circuit

ABSTRACT

An all electronic, tank housed, ballistics computer circuit which upon the receipt of laser BCD range signals from a laser range finder, provides electrical signals containing information which is representative of a plurality of straight line slopes and intercepts so as to electronically approximate a known ballistic function for gun positioning purposes. The received BCD signals are converted to analog ac range and dc range information. The dc range information is utilized with a reference voltage to selectively enable logic circuitry which, when so enabled, permits selected solid stage switches to pass electrically analoged slopes and intercepts developed from the analog ac range information and an ac reference voltage, respectively.

O Umted States Patent [151 3,686,478 Goldberg et al. [451 Aug. 22, 1972[54] ELECTRONIC BALLISTIC COMPUTER 3,551,655 12/1970 Walsh ..235/ 197 XCIRCUIT 3,560,726 2/1971 Platt ..235/197 Inventors: Ira L Schussler PaulM. Marasco, Cherry Hill, N.J.;

- Pn Exanuner-Fehx D. Gruber K nnethR.Pflege armm ,P r e w aAttorney-Harry M. Saragovitz, Edward J. Kelly, Her- [7 Asslgnw The s aAmerlc? bert Berl and Sheldon Kanars nepresen y retary y [57] ABSTRACTFiled: 13, 1970 An all electronic, tank housed, ballistics computer cir-[2i] App. 39,213 cuit which upon the receipt of laser BCD range signalsfrom a laser range finder, provides electrical signals 52 Us Cl 235 61 E89 41 ME 235 150 53 containing information which is representative of al 1 l I plurality of straight line slopes and intercepts so as to lm. Clelectronically approximate a known ballistic function i for gpositioning purposes The received BCD [58] Flew gg i signals areconverted to analog ac range and dc range 23 I E information. The dcrange information is utilized with a reference voltage to selectivelyenable logic circuitry which, when so enabled, permits selected solidstage [56] References Cited switches to pass electrically analogedslopes and inter- UNITED STATES PATENTS cepts developed from the analogac range information 3 575 085 4/1971 McAdam 235/61 5 DP and an acreference voltage, respectively. 33911772 7/1971 McAdam ..235/197 x 3Claim, 4 Drawing Figures ANALOG AG/RhNGE c AG REF V I7 I if 56 I6 4 -'0928 24 g/ 61 36 l 47 4a 4 5' E? SW 32 2 3o 26 l E3s \o 5:42 .4 34

REF 4 Patented Aug. 22, 1972 3,686,478

2 Sheets-Sheet 1 OUTPUT FIG. 2.

FUNCTION GENERATOR OUTPUT OTHER BALLISTIO FUNCTION INPUTS FIG.|.

A0 TO CONV.

I N V ECTORS IRA I. GOLDBERG PAUL M. MARASCO KENNE TH R. PFLEGER mail/m2MM r M v SAJJM 'mmL) ATTORNEYS! ANALOG AG RANGE LASEEJ BOD Patented Aug.22, 1972 2 Sheets-Sheet 2 KENNETHRPFLEGER Mu I an N mm in w 3m 3m mm 2mm mm 27% FOP-.50

2 mm 5 on 4 3w 3w mv ww wv 6 nut 04 9|! ELECTRONIC BALLISTIC COMPUTERCIRCUIT STATEMENT OF GOVERNMENT INTEREST The invention described hereinmay be manufactured, used, and licensed by or for the Government forgovernmental purposes without the payment to us of any royalty.

BACKGROUND OF THE INVENTION This invention relates to an all electronic,ballistics computer circuit for combat vehicle application. Moreparticularly, the invention relates to an electronic, solid state,computer circuit for applying ballistic and lead information to a tankor other military weapon fire control system for gun positioningpurposes. The invention is housed within the tank and is relativelylight, compact, and insensitive to shock and vibration. Prior art tankballistic computer systems, as well as the present invention, mayoperate in conjunction with a tankhoused laser rangefmder. A laser beamis directed toward a target (fixed or moving) and the reflected beam iscollected in an optical system which also electro-optically converts thelaser range data into electrical binary coded decimal (BCD) pulses. TheBCD signals are fed through a digital to analog converter so as toprovide electrical analog range information.

In the prior art systems, this electrical analog information is fed toan electro-mechanical range conversion servo which converts the rangeinformation into an analog shaft rotation. This shaft rotation, is thenutilized to mechanically position the sliders of function potentiometersin the computer, thus inserting the proper range. Servo positioningsignals in elevation and azimuth are likewise generated and aretransmitted to the servo motors of reticle positioning servos in thetelescope or periscope.

While the aforementioned prior art computer is relatively simple, thenecessary use of electro-mechanical elements extremely limits systemperformance. Error is frequently introduced because of wear and tear,slippage, and susceptability to shock and vibration. Also, cost and sizebecome important factors, especially when it is considered that theusable area within a tank is severely limited. In addition, due to thenature of the electro-mechanical elements themselves, the reliability ofthe overall system is low. It has been shown that the mean time betweenfailures (MTBF) of the system is only approximately 300 hours. There hastherefore arisen a need for a tank ballistics computer which does notsuffer from the disadvantages listed above and which is relativelyinexpensive and ideally suited to microminiaturization.

It is therefore the general purpose of the invention to provide an allelectronic, solid state, ballistics computer circuit which is bothrugged and reliable and which, upon the receipt of laser BCD signals,entirely electrically generates gun positioning signals for one of theballistic functions. A ballistic computer containing circuitry accordingto the present invention has an MTBF conservatively stated at 2,000hours. Accuracy and performance have also been greatly enhanced. Beingall electronic, size and cost have been greatly reduced. In additionmicrominiaturization seems applicable thereby affording a greatersavings of space.

SUMMARY OF THE INVENTION A laser rangefinder provides laser BCD pulsesor signals to a digital to analog converter which, responsive thereto,provides electrical analog ac range signals or voltages. The ac rangevoltages are fed through precisely chosen input resistors to a bank ofnormally open switches. An ac reference voltage is likewise fed to alike bank of switches through a second set of precisely chosen inputresistors. The ac range voltages are also converted into dc levels andas such are utilized to preselectively enable logic circuitry which connects supply control or enabling signals to the aforementioned switchbanks. The laser BCD signals enable certain portions of the logiccircuitry to the exclusion of other portions. Those portions that areenabled function to enable certain switch pairs in the switch banks forpassage therethrough of the ac range information (after developmentacross certain of thefirst set of the input resistors) and of the acreference voltage (after development across certain of the second set ofinput resistors). The ac range information developed across the firstset of input resistors provides the slopes while the ac referencevoltage developed across the second set of input resistors provides theintercepts of straight lines utilized to fit or approximate a non-linearballistic function. In this way, a facsimile of the ballistic functionis produced.

DESCRIPTION OF THE DRAWING FIG. 1 is a simplified illustration of aprior art system utilized to position the gun of a military weapon uponthe receipt of range information and the conversion thereof into anangular shaft rotation;

FIG. 2 is a graph of a typical ballistic function;

FIG. 3 is a block diagram of the computer circuit in accordance with thepresent invention; and

FIG. 4 is a more detailed and partially schematic diagram of certain ofthe elements of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT A computer system containingcircuitry according to the present invention provides continuous andsimultaneous analog solutions of the total elevation correction angleand total deflection correction angle ballistic equations. Theseequations may be stated as:

D=, sin C--6 cos C+A 2 where,

E total superelevation above the LOS (Line of Sight) (mils) D= totaldeflection from the LOS (mils) total superelevation correction in thevertical plane for the effects of gravity and differential effects suchas air density, EFC (Effective Full Charge), etc. (mils) o totalhorizontal correction due to ammo drift,

crosswind and the effect of a moving target (mils) C cant angle betweenthe gun trunnion axis and the local horizontal e total elevationcorrection due to gun tube droop,

sighting system parallax, and zeroing (mils) A= total horizontalcorrection for the gun tube bend,

sighting system parallax and zeroing (mils) It is considered unnecessaryto herein discuss the derivation of equations (1) and (2) as they arewell known in the art. Many texts contain this information. See, forexample, Engineering Design Handbook, Fire Control Series, Section I,AMC Pamphlet No. 706-327, January 1968, pages 2-39 through 2-44.

A ballistic computer containing circuitry according to the inventionsynthesizes and instruments the above equations by electricallygenerating facsimiles of each of the ballistic functions which comprisethe terms of the equations. Since the technique can be the same for allof the ballistic functions, only one such instrumentation is hereindisclosed, it being understood that like instrumentation may be employedto electronically synthesize the other ballistic functions.

Referring now to the drawing and more particularly to FIGS. 1 and 2,there is shown respectively therein a prior art system forelectro-mechanically generating the superelevation ballistic function((1),) of equations 1 and 2, and a non-linear graph depicting 4),, as afunction voltage of both angular shaft rotation and range (R).

FIG. 1 includes a potentiometer 9 having a mechanically actuated sliderarm 10 communicating therewith and a plurality of resistor taps ll, ofpreselected ohmic value, one each placed in parallel configurationacross selected lengths of the potentiometer. The potentiometer isgrounded at one end thereof and is connected at the other end to asource of alternating current herein labeled V The output from thepotentiometer 9 connected by slider arm 10 and a wire 13 to a summingoperational amplifier 14 which also receives other ballistic functioninputs. The output of amplifier 14 is connected to gun positioningmechanisms, not shown.

Referring now to FIG. 2, along with FIG. 1, it is known from experiencethat the superelevation ballistic function may be representedgraphically be the essentially non-linear curve F ((1),) plotted withvoltage as the ordinate and range (as an angle) as the abscissa.

It can therefore be seen that for a particular range there 1 correspondsthereto a particular voltage. The system of FIG. 1 utilizes thisapproach by providing the potentiometer 9 with resistor taps 11 ofparticular ohmic value to allow the slider arm 10 to pick off a voltageacross a particular resistance value representative of the slope of thesuperelevation function for a given range to feed that voltage via theline 13 to the summing amplifier 14. Thus, in operation, when receivedlaser BCD signals are converted to a shaft rotation by means of adigital to analog converter and a range conversion servo, as discussedheretofore, the slider 10 is moved up or down the potentiometer 9 as afunction of the amount of angular rotation or range received andtherefor selects a particular resistance across which a voltage dropfrom the supply, V may be developed. This resistance is representativeof the slope of F ((1),) for the particular range R (0). The uniquevoltage developed for this resistance may be applied to the operationalamplifier 14 and would correspond to the superelevation correction forthe particular range. Other ballistic function inputs, as included inthe equations 1 and 2, may be supplied to the amplifier 14 by means ofother, like, potentiometer setups. The resultant total correctionappears at the output of amplifier 14 upon the summation of theballistic function inputs thereby.

As discussed heretofore, this electro-mechanical approach, whilerelatively simplistic in form, was not too reliable clue to the inherentdisadvantages of an electromechanical system. It is apparent, forexample, that vibration and shock, as experienced by a tank, couldgreatly cause the slider 10 to shift and to therefore produce erroneousinformation at the amplifier 14 output.

Referring now to FIG. 3, along with FIG. 2, the present invention willbe explained. In FIG. 3, there is shown a block diagram forelectronically generating a facsimile of the superelevation ballisticfunction F (4),). It is to be understood, of course, that any of theballistic functions which comprise the terms of the equations 1 and 2may be generated in a manner analogous to that hereinafter disclosed.

Received laser BCD signals or pulses are fed to a digital to analogconverter 8 which provides range data in the form of electrical analogac range information. This analog range information is fed directly toan ac to do convertor l5 and, via the line 12, to a function generator16. Convertor 15 provides dc range information along a single wire andthence along four wires to logic circuitry 17, which is connected byfour wires to provide switching signals to the function generator 16.Logic circuitry 17 further receives minus or negative dc referencevoltage via the four lines 18 which connect at a common junction to asingle line leading to the dc reference source and further receives vialines 19 and 20 negative and positive bias voltages indicated as V and+V. Function generator 16 further receives an ac reference voltage viathe line 21 and provides at its output two signals which are anelectronic facsimile of the superelevation function F (tb for aparticular range. These signals are fed to a summing amplifier 22 havingthereacross a feed back resistor 23. The amplifier 22 output is fed toreticle positioning servomechanisms in a periscopic or telescopic sightand/or to gun positioning mechanisms in the tank (not shown).

Referring now to FIG. 4, there is shown in greater I detail the logiccircuitry 17 and function generator 16 of FIG. 3. The logic circuitry isherein shown to comprise a plurality, here four, of operation amplifiers24-27, inclusive. DC range information from the convertor 15 is fed tothe input of each of the amplifiers 24-27 through respective resistors28, 29, 30, and 31. Similarly, the negative dc reference voltage is fedto the same input of amplifiers 24-27 through respective resistors 32,33, 34, and 35. Resistors 28-31, inclusive, have the same ohmic value,whereas resistors 32-35 have significantly different ohmic values forreasons to be explained hereinafter. The outputs of amplifiers 24-27 areconnected respectively to PNP transistors 36-39, inclusive, throughtransistor biasing circuitry 40. The collectors of transistors 36-39receive the -V voltage through resistors 41. The emitters of transistors36-39 are connected to a +V voltage and to ground through resistors 42.The four outputs from the logic circuitry 17 are taken from thecollectors of transistors 36-39 via the lines 43, 44," 45, and 46,respectively. Line 43 is connected to a pair of electronic solid stateswitches 47 and 48 of function generator 16. Similarly, each of thelines 44-46 is connected to a respective like pair of switches 49 and51); 51 and 52; and 53 and 54. Switches 47, 49, 51 and 53 receive analogac range information (via the line 12, as shown in FIG. 3). Placed inthe line 12, are serially connected resistors 56, 57, 58, 59, and 60.Thus, the analog ac range information delivered to the switch 47 isdeveloped across the voltage divider comprised of resistor 56 andresistors 57-60 to ground. Whereas, the analog range informationdelivered to the switch 49 is developed across the voltage dividercomprised of resistor 56, 57 and the series resistance comprisingresistors 58-60 to ground. In like manner, the range informationdelivered to the switches 51 and 53 is developed across voltage dividerscomprising resistor 56 and series combinations of resistors 59 and 60 toground and resistor 60 to ground respectively An ac reference voltage isdeveloped across resistors 61-65 connected in series to ground. Theseresistors are connected to switches 48, 50, 52, and 54 via,respectively, the taps 66, 67, 68 and 69. The outputs of switches 47,49, 51 and 53 are connected, via the line 71, to operational amplifier22 through the resistor 70. Similarly, the outputs of switches 48, 50,52, and 54 are connected, via the line 73, to amplifier 22 throughresistor 72.

It should be understood that the set of resistors 56-60, although shownin a series relationship may also be arranged in a parallelrelationship. In the parallel arrangement the resistance values of eachresistor will be such that the effective resistance of the network willallow the required voltage levels to be passed by the switches 47, 49,51 and 53 to the amplifier 22. Similarly, resistors 61-65 may bearranged in a parallel relationship rather than series.

Referring again to FIG. 2, it is seen that a specific function, here thesuperelevation function F ((1),), can be approximated by a series ofstraight line slopes and intercepts. In FIG. 2, four such straight lines4a,, qb 4), and 41 are shown. It is to be understood, however, that forgreater accuracy it is only necessary to fit more straight lines to theF ((1),) curve. Since for any straight line, (1) AR B where A is theslope and B is the intercept, and further since F ((11,) d), 1) thetotal superelevation ballistic function may be represented by:

That is, the total superelevation ballistic function may be graphicallydepicted by a plurality of straight line segments. The circuitry of FIG.4 electronically mechanizes equation (3), the various slopes beingdetermined by resistors 56-60, inclusive, and switches 47, 49, 51, and53 and the various intercepts being determined by resistors 61-65 andswitches 48, 50, 52, and 54. This will now be described.

As stated heretofore, resistors 32-35, inclusive, have different ohmicvalues. These values are chosen from experience so as to be inconsonance with the received laser BCD signals. By way of example,resistor 35 may be assigned a given value, for example K, with resistors34, 33, and 32 having respectively, the ohmic values 20K, 30K, and 40K.

The operation of the system is as follows. As noted heretofore, rangeinformation in the form of laser BCD signals are converted into analogac range information and further converted into dc range information (byconverter As shown in FIG. 4, this dc range information is fed toresistors 28-31, inclusive, all of which may be considered to have thesame ohmic value. When the dc range signal is zero, the only voltageappearing at the input of respective amplifiers 24-27 is a negative onedue to the negative dc reference voltage applied across respectiveresistors 32-35, inclusive. When a negative voltage is present at arespective amplifier input, the amplifier provides a positive output dcvoltage which may, for explanation purposes, be plus 10 volts. Thisvoltage is applied to the respective PNP transistors 36-39, inclusive,which invert the received signal to provide a negative 10 volt signal tothe respective switches in the function generator 16. Switches 47-54,inclusive, may comprise any of the known, solid state electronic typesas, for example, field effect transistors, which are rendered operativeupon the receipt of a control signal which is positive in sense. Hencethe receipt by these switches of a negative signal maintains theswitches in their off or non-conductive state. Furthermore, theseswitches rather than being electronic, may be activated by any meanswhich will cause a switch to open or close. These means may be, but arenot limited to, electromechanical, mechanical, magnetic, hydraulic,pneumatic or fluidic.

As the dc range signals supplied to the logic circuitry are increased, aparticular one of the amplifiers 24-27 will have applied thereto aslightly positive input. The presence of a positive input will cause theamplifier to provide a negative 10 volt output which will cause thetransistor associated therewith to provide a positive 10 volt output.This last-mentioned positive voltage will cause the particular connectedswitch pair in the function generator 16 to be rendered conductive. Thecontrolled or ac analog range information received via the line 12 andmodified by voltage divider comprised of resistor 56 and a series of theresistors 57-60, inclusive, is then passed by the now conductive switchthat is oddnumbered. Similarly, at the same time that this switch isrendered conductive (as for example switch 47), its companion switch (orswitch 48) is likewise rendered conductive by the positive 10 voltsignal with the result that switch 48 passes the ac reference signal viathe ohmic drop across the voltage divider formed by re sistors 61-65 asdetermined by the arm 66. In this way, the slope and the intercept,respectively, for one of the straight lines shown in FIG. 2 are fed tosumming amplifier 22.

The particular amplifier or amplifiers which is (are) rendered operativeto provide the aforementioned switching signals is determined by theohmic values of resistors 32-35, inclusive. Thus, recalling thatresistors 32-35 are assigned the values respectively of 40K, 30K, 20K,and 10K and assuming that the negative dc reference voltage applied isminus volts, the following becomes apparent. The current throughresistor 32 is -3 ma while the current through the remaining resistorsis 4 ma for resistor 33, -6 ma for resistor 34, and -12 ma for resistor35. Resistors 28-31 have the same ohmic value and consequently, a netzero voltage will be present at the input of the amplifiers 24-27 whenthe current passing through resistors 28-31 (as developed by the dcrange voltage) balances out or bucks the current through the resistors32-35.

Thus, as the dc range voltage rises from zero the amplifier 24 will havea net zero voltage at the input thereof when the current throughresistor 28 is sufficient to balance out the 3 ma flowing throughresistor 32. Any slighter rise in do range voltage will render theamplifier 24 input positive to cause the amplifier 2d to provide the lvolt output signal as aforementioned thereby eventually renderingswitches 47 and 4% conductive. With respect to the amplifier 27, the dcrange voltage must rise to a level such that it bucks out -12 It is thusseen that as the dc range information rises from zero to some positivelevel or levels as a function of the received BCD laser range signals,amplifier 24 is the first to have a net zero voltage input appliedthereto, amplifier 27 the last, and amplifiers 25 and 26 are second andthird, respectively. Since each of the amplifiers 24-27 provide anegative output upon the presence of just slightly greater than a zeroinput, it is seen that switches 47 and 4-8 are the first pair to switch,switches 49 and 50 are the second pair, switches 51 and 52 the third,and switches 53 and 54 are last. Thus, by realizing the switchingsequence and by properly choosing the ohmic values of resistors 56-60,inclusive it becomes possible to select straight line slopes which willfit the ballistic function of FIG. 2.

Thus the slopes of (1),, (1);, and d), are herein determined by thevoltage divider comprised of resistors 56-60. In like manner, properpositioning of the arms 66-69, inclusive, of the voltage dividercomprised of resistors 61-65 permits the selection of the desiredintercept.

It is to be noted that the series of discrete resistors 6l-65 couldquite readily be replaced by a single resistor tapped at the appropriatepoints.

It has thus been shown that the switch pairs 47 and 48 and theresistance associated therewith provides one of the aforementionedstraight lines (for example, 4).) utilized to generate thesuperelevation ballistic function. The remaining switch pairs and theirremaining associated resistances in conjunction with the pairs andresistors already switched may be utilized to generate the remainingstraight lines. Greater accuracy could be achieved merely by connectingadditional switch pairs in the manner of connection shown in FIG. 4.

The remaining ballistic functions comprising the terms of equations (1)and (2) may be instrumented in the manner analogous to thataforedescribed. All that is required is a repetition of the samecircuitry for each of the functions. It is further noted, however, thatby manipulation of the above equations it becomes ap parent that certainof the electrical elements can be shared so as to effect a reductionand/or savings in parts.

For positioning the reticle of a periscopic or telescopic sight, and/orthe tank gun, it is necessary only to sum the outputs from the variousfunction generators, as for example, by a summing amplifier such asamplifier 22, and to feed the output thereof to reticle or gunpositioning mechanisms in the tank.

We wish it to be understood that we do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

We claim:

1. An electronic ballistic computer circuit for generating a ballisticfunction in the process of positioning the gun of a military weapon uponthe receipt of range finder signals and the conversion thereof intoelectrical pulses, comprising:

means receiving the electrical pulses for providing ac analog voltagesresponsive thereto and representative thereof;

conversion means connected to said receiving means for providing dcvoltages upon the receipt thereby of said ac analog voltages;

logic means connected to said conversion means for providing switchcontrol signals upon the receipt of said dc voltages, a referencevoltage, and positive and negative bias voltages;

function generating means connected to said logic means and saidreceiving means for providing signals representative of an electricalfacsimile of a ballistic function upon the receipt of said ac analogvoltages and said switch control signals;

means connected to said function generating means for providing gunpositioning signals upon the receipt of said electrical facsimilesignals, and

means connected to said function generating means for providing an acreference voltage thereto, and

wherein said reference voltage provided to said logic means is anegative dc voltage, and said function generating means comprises:

a first plurality of switches for receiving said switch control signals;

a second plurality of switches for also receiving said switch controlsignals;

a first voltage divider resistor network connected to said first switchplurality and receiving said ac analog voltage for offering preselectedamounts of ohmic resistance thereto to control the voltage levelssupplied to each switch of said first plurality,

a second voltage divider resistor network connected to said secondswitch plurality and receiving said ac reference voltage for offeringpreselected amounts of ohmic resistance thereto to control the voltagelevels supplied to each switch of said second plurality, and

wherein said first and second switch pluralities respectively passselected levels of said ac analog voltages and said ac reference voltageupon the receipt of said switch control signals.

2. A function generator for providing an electrical facsimile of aballistic function upon the receipt of ac analog range and ac referencevoltages and further upon the receipt of dc range switching signals,comprismg:

first and second pluralities of switches connected to receive saidswitching signals;

first and second voltage dividers connected respectively to said firstand second switch pluralities for respectively offering preselectedamounts of ohmic resistance to said analog voltages and said acreference voltages to control the voltage levels supplied to each switchof said switch pluralities, and

wherein selected switches of said first and second switch pluralitiespass selected levels of said ac analog voltages and said ac referencevoltages upon the receipt of said switching signals;

said first switch plurality and said second switch plurality comprise alike number of switches;

3. A function generator for providing an electrical facsimile of aballistic function upon the receipt of ac analog range and ac referencevoltages and further upon the receipt of dc range switching signals, asdescribed in claim 2, wherein said second voltage divider comprises:

a plurality of series-connected resistors connected to receive said acreference voltages, each of said last mentioned resistors of preselectedohmic value and each connected to at least one switch of said secondswitch plurality.

1. An electronic ballistic computer circuit for generating a ballisticfunction in the process of positioning the gun of a military weapon uponthe receipt of range finder signals and the conversion thereof intoelectrical pulses, comprising: means receiving the electrical pulses forproviding ac analog voltages responsive thereto and representativethereof; conversion means connected to said receiving means forproviding dc voltages upon the receipt thereby of said ac analogvoltages; logic means connected to said conversion means for providingswitch control signals upon the receipt of said dc voltages, a referencevoltage, and positive and negative bias voltages; function generatingmeans connected to said logic means and said receiving means forproviding signals representative of an electrical facsimile of aballistic function upon the receipt of said ac analog voltages and saidswitch control signals; means connected to said function generatingmeans for providing gun positioning signals upon the receipt of saidelectrical facsimile signals, and means connected to said functiongenerating means for providing an ac reference voltage thereto, andwherein said reference voltage provided to said logic means is anegative dc voltage, and said function generating means comprises: afirst plurality of switches for receiving said switch control signals; asecond plurality of switches for also receiving said switch controlsignals; a first voltage divider resistor network connected to saidfirst switch plurality and receiving said ac analog voltage for offeringpreselected amounts of ohmic resistance thereto to control the voltagelevels supplied to each switch of said first plurality, a second voltagedivider resistor network connected to said second switch plurality andreceiving said ac reference voltage for offering preselected amounts ofohmic resistance thereto to control the voltage levels supplied to eachswitch of said second plurality, and wherein said first and secondswitch pluralities respectively pass selected levels of said ac analogvoltages and said ac reference voltage upon the reCeipt of said switchcontrol signals.
 2. A function generator for providing an electricalfacsimile of a ballistic function upon the receipt of ac analog rangeand ac reference voltages and further upon the receipt of dc rangeswitching signals, comprising: first and second pluralities of switchesconnected to receive said switching signals; first and second voltagedividers connected respectively to said first and second switchpluralities for respectively offering preselected amounts of ohmicresistance to said analog voltages and said ac reference voltages tocontrol the voltage levels supplied to each switch of said switchpluralities, and wherein selected switches of said first and secondswitch pluralities pass selected levels of said ac analog voltages andsaid ac reference voltages upon the receipt of said switching signals;said first switch plurality and said second switch plurality comprise alike number of switches; said switching signals are provided to selectedpairs of switches, one each in each of said switch pluralities, wherebyone or more of said switch pairs may be rendered operative to pass saidac analog voltages and said ac reference voltages to the exclusion ofthe remaining switches in said switch pluralities, and said firstvoltage divider comprises a plurality of series-connected resistorsconnected to receive said ac analog voltages, each of said resistors ofpreselected ohmic value and each connected to at least one switch ofsaid first switch plurality.
 3. A function generator for providing anelectrical facsimile of a ballistic function upon the receipt of acanalog range and ac reference voltages and further upon the receipt ofdc range switching signals, as described in claim 2, wherein said secondvoltage divider comprises: a plurality of series-connected resistorsconnected to receive said ac reference voltages, each of said lastmentioned resistors of preselected ohmic value and each connected to atleast one switch of said second switch plurality.